1. Field of Invention
This invention relates to a sensing device for use in high-speed continuous paper feeding printing presses. In particular, the invention relates to a hub speed sensor for a roll of paper for use in a system which automatically joins the newsprint of a spent web to the newsprint of a fresh web in an operating printing press environment.
High volume presses, such as letterpress type presses used in newspaper printing, require continuous feed of newsprint. A press run generally consumes much more paper than is provided in a single roll of newsprint. In order to prevent frequent disruption of press runs, machines have been developed for automatically joining fresh newsprint webs to spent webs during a press run while newsprint if feeding at a rate of several hundred feet per minute. A letterpress having a press feeding system with this capability is the Goss brand continuous roll newspaper printing presses manufactured by MGD Graphic Systems of Chicago, Il.
The Goss type newspaper presses have a web feeding system employing a three pointed star wheel assembly having three hubs for supporting three webs of newsprint. The star wheel assembly is rotated about a central axis so that at any one time a first web can be feeding, a second web can be standing by and a third web, if spent, can be unloaded and the hub can be reloaded with a fresh web.
In operation, a newsprint web feeds at such a high speed that a mechanism must be provided for automatically sensing the approaching exhaustion of a web and for automatically attaching the fresh web to the nearly spent web. This process operates as follows. A sensor is provided to sense the impending run-out of the newsprint web in feed to the presses. At a predetermined signal or series of signals prior to web run-out, the second newsprint web is rotated on the star wheel assembly into a position in near tangent to the newsprint feed path. The fresh web is spun up to feed speed and synchronized with the newsprint feed. At a second signal or predetermined set of signals indicating speed and position synchronism between the beginning of the fresh web and the newsprint feed path, the newsprint feed is slapped against the second web and cleaved from the nearly exhausted feed web. The pressure against the second web causes an adhesive paste on the beginning of the second web to seize the end of the newsprint feed of the previous web, thereby providing an uninterrupted newsprint feed. The exhausted web of the star wheel can thereafter be removed and the hub can be reloaded so that a fresh web is available for subsequent use.
2. Description of the Prior Art
A hub speed sensor, or paster pilot sensor, is critical to the accurate operation of the changeover from a spent web to a fresh web. The hub speed sensor, called a paster pilot sensor, is provided at each web hub of the star wheel. The hub speed sensor operates like a tachometer to provide a signal to a central controller which directs changeover operation. However, the hub speed sensor is both speed and position sensitive. In the prior art, the continuous high-speed presses have employed a commutator brush assembly with rotary contacts of selected lengths to generate needed hub speed and position signals. The previously known commutator brush hub speed sensor required frequent maintenance and has been subject to frequent mechanical failures due to contact wear and exposure to ambient contaminants. Due to the high rotational speed and relatively heavy daily use, contacts wear out quickly, causing loss of signal and occasionally expensive and time consuming press run breakdowns. Consequently there is a need for a reliable hub speed sensor.